The present invention relates to a light emitting apparatus such as headlamps and fog lamps which are equipped on an automotive vehicle.
Further, the present invention relates to a polarized light splitting device and an automotive light emitting apparatus, and more particularly to a polarized light splitting device for splitting non-polarized light emitted from a light source into p polarized light and s polarized light and an automotive light emitting apparatus having the polarized light splitting device.
Headlamps and fog lamps equipped on a vehicle are such as to be illuminated when there occurs a situation where conditions ahead of the vehicle become difficult to be identified. For example, the headlamps are used at night or in a tunnel where surrounding conditions are invisible due to darkness, or when the vision in front gets worse due to heavy rain or thick fog.
Incidentally, in the event that the headlamps of the vehicle are illuminated at the time of thick fog or heavy rain, light emitted from the headlamps are reflected irregularly by rain drops or particles of fog, there occurs a situation where a wall of light, as it were, appears in front of the vehicle, and the vision in front is interrupted.
FIG. 14 shows a condition of light emitted from the headlamps of the vehicle at the time of thick fog or heavy rain, in which FIG. 14A is an exemplary diagram illustrating a distribution of light from the headlamps in such a condition, and FIG. 14B is an exemplary diagram illustrating an irregular reflection produced on the surfaces of rain drops at the time of heavy rain.
As shown in FIG. 14A, since light emitted from the headlamps is irregularly reflected in a complex fashion on the surfaces of fine particles of vapor or rain drops which exist on the optical paths and forms a wall of light in the vicinity of the vehicle, the driver cannot secure the vision in far front of the vehicle.
As shown in FIG. 14B, light is reflected repeatedly and in various direction on the surfaces of rain drops, and the driver feels that there appears a wall of light due to rain drops illuminated by the headlamps. In a condition like this, an object which can be identified in a normal condition cannot be identified.
Here, while rain drops falling at the time of thick fog or heavy rain are formed into a substantially spherical shape, as the particle shape becomes larger, rain drops are subjected to larger air resistance and becomes flat, whereby the surface area of such rain drops is increased. Since rain drops are fanned into such a shape, light from the headlamps which enters sideways is irregularly reflected in various ways and is then diffused in a vertical direction relative, in particular, to the ground. Furthermore, since the density of rain drops is increased at the time of thick fog or heavy rain, light irregularly reflected once by rain drops is reflected again by lots of rain drops existing in the vicinity of the original rain drops, and thus, the reflection is repeated, whereby rain drops in the whole area illuminated by light emitted from the headlamps are illuminated, so that the driver feels as if there appears a wall of light in the vicinity of the vehicle, and the vision in front of the driver is interrupted, the vision in far front of the vehicle thereby becoming difficult to be identified by the driver.
Incidentally, there exists an invention for interrupting light from headlamps by incorporating polarizer in headlamps of a vehicle (for example, refer to JP-A-61-253236 (page 2, FIGS. 1 to 3)). This invention is intended to prevent the dazzle of the driver by the headlamps in high-beam conditions, and a polarizer is incorporated in a high-beam lamp of the headlamp and a light detector is incorporated in a windscreen, so that the driver is prevented from being dazzled by high beams from an oncoming vehicle.
JP-A-61-253236 (page 2, FIGS. 1 to 3)
Further, conventionally, there are disclosed polarized light splitting devices for improving the utilization rate of light emitted from a light source by laminating alternately high refractive index films and low refractive index films (for example, refer to JP-A-9-293406 (pages 4 to 5, FIG. 1 and FIGS. 8 to 12)).
A polarized light splitting device described in JP A-9-293406 (pages 4 to 5, FIG. 1 and FIGS. 8 to 12) is a polarizing plane light source device in an image display using linear or plane polarization such as a general purpose liquid crystal display.
Here, the polarized light splitting device is such that a polarized light splitting layer is formed by two to six transparent films comprising glass as a high refractive index film, a polyester film and a polyphenol A polycarbonate film.
In addition, a light emitting apparatus fitted on an automotive vehicle such as a headlamp and a fog lamp is such as to illuminate when there occurs a situation where a condition in front of the vehicle becomes difficult to be identified by the naked eyes of the driver.
Then, in order to improve the vision in front of the vehicle by eliminating the problem, it is conceivable to adopt the polarized light splitting device described in JP A-9-293406 (pages 4 to 5, FIG. 1 and FIGS. 8 to 12) for the automotive light emitting apparatus.
Namely, it can be contemplated to improve the utilization rate of light emitted from the light source so as to brightly illuminate the front of the vehicle.
However, in the invention described in JP-A-61-253236 (page 2, FIGS. 1 to 3), since light emitted from the headlamp is cut due to the utilization of the polarizer (a polarizing filter), 50% or more of the light so emitted is lost and this reduces the utilization efficiency of headlamp light, causing a problem that the illuminated area gets dark.
Due to this, in the event that such headlamps are used at the time of thick fog or heavy rain, the illuminated area in front of the vehicle gets darker.
Namely, with the headlamps according to JP-A-61-253236 (page 2, FIGS. 1 to 3), it is not possible to illuminate brightly the area in front of the vehicle, and since the invention is not intended to cope with a case where the vision of the driver is interrupted by thick fog or heavy rain, the invention can provide no effect to improve the vision at the time of thick fog or heavy rain.
In addition, since the polarizer (the polarizing filter) has in general a low heat resistance, in the event that it is used in the headlamp, there is caused a problem that the polarizing performance of the polarizer heated by the heat of the headlamp is deteriorated drastically.
Furthermore, in a case where the light emitting apparatus is used as an automotive headlamp, due to the configuration of a location of a vehicle where the headlamp is disposed or the construction of the light emitting apparatus, there have exsisted limitations not only on the disposition of the headlamp but also on the design of vehicles.
Further, in a case, however, where the polarized light splitting device in JP A-9-293406 (pages 4 to 5, FIG. 1 and FIGS. 8 to 12) above where the high refractive index films and the low refractive index films which comprise the solids such as transparent films are laminated is used for an object which is subjected to vibration during traveling such as a vehicle, there is expected a deformation or deviation between the high refractive index film and the low refractive index film.
Consequently, since the refractive indices and the direction of reflection are changed due to such a deviation between the laminated films in the laminated layer, there is caused a problem that proper refraction and reflection of light cannot be attained, and hence, splitting into appropriate polarized light cannot be attained.
It is desired that the polarized light splitting device and the automotive light emitting apparatus equipped with the polarized light splitting device need to be maintained in a condition where enough durability to eliminate the occurrence of any deformation or deviation in position that would be caused between the high refractive index film and the low refractive index film in the polarized light splitting device by vibrations, so that proper refraction and reflection of light and splitting into appropriate polarized light can be attained at all times.